Tunable optical fiber connector

ABSTRACT

An optical fiber connector that is tunable despite being fully assembled has a assembly having an enlarged ferrule holding member or flange that has a multi-faceted periphery, preferably in the shape of a hexagon. The connector has a front housing portion that has a multi-faceted seating region for the flange. The flange is disengageable from the seating region for tuning rotation by being movable axially toward the rear of the housing against the force of a spring. The connector can be tuned by incremental rotations of the assembly when the flange is disengaged.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.09/363,908 and Ser. No. 09/362,203, both filed concurrently herewith.

FIELD OF THE INVENTION

This invention relates to an optical fiber connector and, moreparticularly to a to tunable optical fiber connector.

BACKGROUND OF THE INVENTION

In optical fiber communications, connectors for joining fiber segmentsat their ends, or for connecting optical fiber cables to active orpassive devices, are an essential component of virtually any opticalfiber system. The connector or connectors, in joining fiber ends, forexample, has, as its primary function, the maintenance of the ends in abutting relationship such that the core of one of the fibers is axiallyaligned with the core of the other fiber so as to maximize lighttransmissions from one fiber to the other. Another goal is to minimizeback reflections. Such alignment is extremely difficult to achieve,which is understandable when it is recognized that the mode fielddiameter of, for example, a singlemode fiber is approximately nine (9)microns (0.009 mm). Good alignment (low insertion loss) of the fiberends is a function of the alignment, the width of the gap (if any)between the fiber ends, and the surface condition of the fiber ends, allof which, in turn, are inherent in the particular connector design. Theconnector must also provide stability and junction protection and thusit must minimize thermal and mechanical movement effects.

In the present day state of the art, there are numerous, different,connector designs in use for achieving low insertion loss and stability.In most of these designs, a pair of ferrules (one in each connector),each containing an optical fiber end, are butted together end to end andlight travels across the junction. Zero insertion loss requires that thefibers in the ferrules be exactly aligned, a condition that, given thenecessity of manufacturing tolerances and cost considerations, isvirtually impossible to achieve, except by fortuitous accident. As aconsequence, most connectors are designed to achieve a useful,preferably predictable, degree of alignment, some misalignment beingacceptable.

Alignment variations between a pair of connectors are the result of theoffset of the fiber core centerline from the ferrule centerline. Thisoffset, which generally varies from connector to connector, is known as“eccentricity”, and is defined as the distance between the longitudinalcentroidal axis of the ferrule at the end face thereof and thecentroidal axis of the optical fiber core held within the ferrulepassage and is made up of three vectors. It is often the case,generally, that the ferrule passage is not concentric with the outercylindrical surface of the ferrule (vector I), which is the referencesurface. Also, the optical fiber may not be centered within the ferrulepassage (vector II whose magnitude is the diametrical difference dividedby two) and, also, the fiber core may not be concentric with the outersurface of the fiber (vector E). Hence eccentricity can be the result ofany one or all of the foregoing. The resultant eccentricity vector hastwo components, magnitude and direction. Where two connectors areinterconnected, rotation of one of them will, where eccentricity ispresent, change the relative position of the fibers, with a consequentincrease or decrease in the insertion loss of the connections. Where themagnitude of the eccentricities are approximately equal the directioncomponent is governing, and relative rotation of the connectors untilalignment is achieved will produce maximum coupling.

There are numerous arrangements in the prior art for “tuning” aconnector, generally by rotation of its ferrule, to achieve an optimumdirection of its eccentricity. One such arrangement is shown in U.S.Pat. No. 5,481,634 of Anderson et al., wherein the ferrule is heldwithin a base member which maybe rotated to any of four rotational oreccentricity angular positions. In U.S. Pat. No. 4,738,507 of Palmquistthere is shown a different arrangement and method for positioning twoconnectors relative to each other for minimum insertion loss or maximumcoupling. The arrangements of these patents are examples of the effortsto achieve optimum reliable coupling, there being numerous otherarrangements and methods.

In all such arrangements for achieving optimum coupling with connectorshaving different magnitudes and directions of eccentricities, the tuningtakes place, usually, if not always prior to the final assembly of theconnector. As a consequence, an installer in the field has no controlover the degree of coupling, other than by trial and error. Further,tuning of the connector cannot be performed after production of theconnector is completed. Thus tuning prior to final assembly of theconductor is a step in the production process.

An optical fiber connector that can be tuned for optimum performanceafter the connector has been assembled would greatly decrease productioncosts and further, impart a greater measure of reliability to theconnectors. Such a connector would be of significant commercial value.

SUMMARY OF THE INVENTION

The present invention is a connector for abutting one optical fiber toanother, and which is tunable for achieving maximum possible signaltransmissivity or minimum insertion loss despite being fully assembled.In a preferred embodiment of the invention the principles thereof areillustrated in a connector of the LC type for single mode fibers. It isto be understood that the principles of the invention are applicable tonumerous other types of connectors such as, for example, the SC, FC andST type connectors, as well as to other fiber optic type devices.

The connector of the invention, which, for purposes of illustration is amodified LC type connector, has the basic components such as are shownin U.S. Pat. No. 5,481,634 of Anderson et al., the disclosure of whichis incorporated by reference herein.

The basic components of such a connector as shown in the Anderson et al.patent comprises a assembly for holding the end of an optical fiberextending axially therethrough and a plug housing member which containsthe assembly. A coil spring member contained within the housingsurrounds the barrel and bears against an interior wall of the housingand an enlarged barrel member or flange, thereby supplying forward biasto the barrel-ferrule assembly relative to the housing. The barrelmember, referred to as a flange in the Anderson et al. patent, is shapedto be supported within an interior cavity within the housing in any oneof four rotational orientations with respect to the central axis of thefiber holding structure. A ferrule extends axially from the enlargedbarrel member and contains a fiber end therein. Thus the direction ofeccentricity of the fiber relative to the central axis can have any oneof four rotational or angular orientations. The connector is “tuned” tothe extent that four orientations are possible. However, the “tuning” isa manufacturing step preceding final assembly of the connector, afterwhich it is no longer “tunable”.

In accordance with the present invention, the barrel-ferrule assembly ofthe connector is modified so that the enlarged barrel member isoptimally hexagonal in shape, and has a tapered or chamfered leadingsurface which may be slotted. The housing is also modified so that theinterior cavity is hexagonal in shape to accommodate the barrel memberin any of six rotational orientations and a sloped constriction againstwhich the leading surface bears in its forward position. Tuning of thefully assembled connector is accomplished by the application of an axialforce to the barrel member, as by a spanner wrench fitted within theslots in the leading surface, sufficient to overcome the bias of thecoil spring and to push the barrel portion rearwardly out of engagementwith the hexagonally shaped recess in the housing and the slopedconstriction. The assembly is then rotatable to any of six angularorientations, sixty degrees (60°) apart. It should be noted that alesser number of surfaces can be used if the diagonal distance of thebarrel cross-section is reduced sufficiently to allow rotation thereofwithin the plug housing. Alternatively, the bore containing the flangemay have an increased diameter, but this tends to weaken the housingwalls. Fewer surfaces, however, means larger increments of rotation andhence less precise reduction in loss. Also, more than six surfaces maybe used, however, the improvement over six surfaces is slight and theclearance surrounding the barrel makes limiting rotation within thehousing difficult to achieve.

The connector may be mated with another connector having a known offset,for example, and insertion loss measurements made after each incrementalrotation. When the angular position yielding the least loss isdetermined, the ferrule-barrel assembly is rotated to that position.

An indexable tuning test tool having a spring loaded split LC adapterthat is keyed and labeled to measure the optical performance of an LCconnector at six different angular orientations is designed for use indetermining the degree of tuning of the connector that is necessary. Thetool has a longitudinal split ceramic sleeve therein for aligning two LCconnector end faces. In operation, a test jumper cable having an LCconnector which has an eccentricity of a magnitude greater than that ofthe connector to be tuned and a known direction (angular orientation),is inserted into the sleeve and the production jumper connector isfitted into the sleeve so that the connector ferrule ends abut. Theopposite end of the jumper cable is connected to an optical source, oran optical detector, and the production jumper is connected to a sourceor detector to complete a test circuit. Ideally, the test jumper has aneccentricity of 1.8 to 3.5 μm relative to the ferrule axis, and has anangular orientation of zero degrees (0°) or one hundred eighty degrees(180°), preferably the former which is an upright vertical orientation.Insertion loss measurements are then taken and the initial loss isnoted. The portion of the tool holding the product jumper is springloaded to allow separation of the fiber end faces and rotation thereof.The tool is thus rotated in sixty degree (60°) increments, with measuredinsertion loss being recorded at each increment. The angular orientationof the product jumper that yields minimum insertion loss is thusdetermined. The labeling on the tool indicates how many degrees, insixty degree increments, the product jumper had to be rotated to produceminimum insertion loss. Inasmuch as the angular orientation of theconnector of the test jumper is known, preferably, as statedhereinbefore, zero degrees (0°) or straight up or vertical, the toolindicates how many incremental stages the product jumper requires tohave a corresponding vertical orientation. It is also feasible toascertain, instead of minimum insertion loss, the angular orientationfor maximum insertion loss. Rotation of 180° from this orientationyields the orientation for minimum insertion loss. In both methods, oneor the other of the extremes of insertion loss is determined.

As an adjunct of the tuning test operation, a tool used for tuning inthe form of a spanner wrench is designed to tune the product connectoron the basis of the test results. The tuning tool wrench comprises anenlarged handle shaped, such as hexagonally, for gripping from whichextends a hollow sleeve having a distal end with first and second tangsextending therefrom. The sleeve is adapted and sized to fit over theferrule of the product jumper connector with the tangs engaging theslots in the leading or front surface of the barrel member. In use, thetangs are engaged and the assembly is pushed to the rear out ofengagement with the plug housing and against the spring bias, so thatthe assembly may be rotated the required number of degrees as indicatedby the tuning index tool to the angular orientation yielding minimuminsertion loss where the connector is mated with another connectorhaving vertical orientation of its eccentricity. The spanner wrench hasa shoulder from which the sleeve extends, which butts against thehousing to limit the insertion distance of the wrench. The distance fromthe face of the shoulder to the tangs is chosen such that the assembly,when pushed against the coil spring, does not cause the spring tobottom, which can be damaging to the spring. The barrel is then rotatedto the tuned position. When the wrench is removed, the spring returnsthe barrel forward to its new rotated seating position. In this manner,the product connector is tuned. It is contemplated that all matingconnections will have such a vertical orientation, hence the installer,for example, does not have to be concerned with optimum tuning.

Thus the unique structure of the connector permits tuning of theassembled connector. Further, the tuning tool enables additionalrotations of the assembly when desired, for whatever reason.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of the components of theconnector;

FIG. 2 is a perspective view of the assembled connector;

FIG. 3a is a front elevation view of the connector housing, frontportion;

FIG. 3b is a cross-sectional side elevation view of the front portion;

FIG. 3c is a front elevation view of the connector housing firstportion, adapted to receive the ferrule-barrel assembly of FIGS. 4c and4 d;

FIG. 4a is a side view of a modified ferrule-barrel member of theconnector;

FIG. 4b is a front elevation view of the member of FIG. 4a;

FIG. 4c is a side elevation view of a modification of the ferrule-barrelassembly of FIG. 1 or FIG. 4a;

FIG. 4d is a front elevation view of the assembly of FIG. 4c;

FIG. 5a is a side elevation cross-sectional view of the connector;

FIG. 5b is a side elevation cross-sectional view of the connector in itstuning configuration;

FIG. 6 is a graph of the effect of offset between two fiber ends;

FIG. 7 is a bar chart of the distribution of insertion loss for untunedconnectors;

FIG. 8 is a bar chart of the distribution of insertion loss for tunedconnectors;

FIG. 9 is an exploded perspective view of a tuning index tool;

FIG. 10 is a side view of the test tool of FIG. 9 as assembled;

FIG. 11 is a cross-sectional view of the tool along the lines A—A ofFIG. 10;

FIG. 12 is a perspective view of the assembled tool;

FIG. 13 is a perspective view of the tuning index tool of FIG. 10 asused in performing tuning tests;

FIG. 14a is a perspective view of the tuning wrench of the invention fortuning a connector;

FIG. 14b is a front elevation view of the wrench of FIG. 14a;

FIG. 14c is a cross-sectional view of the wrench of FIG. 14b along theline B—B;

FIG. 14d is a cross-sectional view of the wrench of FIG. 14b along theline A—A;

FIG. 14e is a detail of the tuning operation using the wrench of FIG.14b; and

FIG. 14f is a cross-sectional view of the connector of the invention asit is being tuned by the wrench.

DETAILED DESCRIPTION

FIG. 1 is an exploded perspective view of the principal components of anLC type connector 11 which embodies the principles of the presentinvention. It is to be understood that these principles are alsoapplicable to other types of connectors, such as an ST, SC, or othersamenable to modification to incorporate these principles. Connector 11comprises a plug housing formed of a front section 12 and a rear section13 having an extended portion 14 which fits into section 12 and latchesthereto by means of slots 16—16 in front section 12 and latching members17—17. Members 12 and 13 are preferably made of a suitable plasticmaterial. Member or front section 12 has a resilient latching arm 18extending therefrom for latching the connector 11 in place is areceptacle or adapter. Member or section 13 has extending therefrom aresilient arm or trigger guard 19, the distal end of which, when the twosections 12 and 13 are assembled, overlies the distal end of arm 18 toprotect it from snagging and to prevent nearby cables from becomingentangled. Usually latch arm 18 and guard 19 are molded with theirrespective housing sections 12 and 13, respectively, and form “livinghinges” therewith, which enable them to be moved up and down betweenlatching and unlatching positions. Front section 12 has a bore 21extending therethrough which, when the parts are assembled, iscoextensive with a bore 22 extending through rear section 13. The bores21 and 22 accommodate a assembly 23 which comprises a hollow tubularmember 24 having a ferrule holding apparatus shown here as an enlargedflange or barrel member 26 from which extends a ferrule 27 which may bemade of a suitably hard material such as, preferably, ceramic, glass, ormetal. Ferrule 27 has a bore 28 extending therethrough for receiving andholding an optical fiber therein. When the connector 11 is assembled, acoil spring 29 surrounds the tubular portion 24 of the assembly 23, withone end bearing against the rear surface of flange 26 and the other endbearing against an interior shoulder in rear section 13, as will best beseen in subsequent figures.

In practice, the uncoated portion of the optical fiber is inserted intobore 28 of ferrule 27 and adhesively attached thereto. Spring 29 iscompressed as the sections 12 and 13 are connected and supplies aforward bias against the rear of flange 26 and, hence, to ferrule 27.This arrangement of ferrule 27 and spring 29 is considered to be a“floating” design. Prior to connection, the spring 29 causes ferrule 27to overtravel its ultimate connected position. When connector 11 isconnected within a suitable adapter and the distal end of ferrule 27butts against the corresponding ferrule end of another connector or ofother apparatus, spring 29 will be compressed, thereby allowing backwardmovement of ferrule 27 to where its end, and the end of the abuttingferrule, lie in the optical plane (transverse centerline) between thetwo connectors.

The rear end of rear section 13 has a ridged member 31 extendingtherefrom for attachment of optical fiber cable and a strain reliefboot, not shown,. For protection of the distal end of ferrule 27 duringhandling and shipping, a protective plug 32, sized to fit within bore21, is provided. FIG. 2 depicts the assembled connector 11 in itsshipping or handling configuration.

In accordance with the present invention, as best seen in FIGS. 4a and 4b, flange 26 has a hexagonally shaped portion 33 and a front taperedportion 34 which can be tapered extension of the hexagon shape. Whilethe following discussion relates to a multi-faceted ferrule holdingmember, it is to be understood that the term “faceted” is intended toinclude other locating arrangements such as, for example, slots orsplines. Front section 12 has a flange seating opening 36 formed in atransverse wall 37 thereof which has a hexagonally shaped portion 38 anda tapered portion 39 dimensioned to receive and seat flange 26, as bestseen in FIGS. 3a and 3 b. In FIG. 3c, the opening 36 has instead of ahexagonal shape, a plurality of splines 40 extending inwardly therefrom,a modification especially adapted to receive the ferrule-barrel assemblyof FIGS. 4c and 4 d. That portion 41 of bore 21 immediately to the rearof portion 38 has a diameter sufficient to allow rotation of flange 26when it is pushed to the rear and disengaged from the seat 36. Thus, aswill be discussed more fully hereinafter, when flange 26 is pushed tothe rear (against the force of spring 29) it may be rotated and, whenreleased, re-seated with tapered portion 34 acting as a guide andcentering arrangement. The hexagonal configuration makes it possible toseat the flange 26 in any of six angular rotational positions, eachsixty degrees (60°) apart. It has been found that a flange having fewerthan six sides cannot be rotated in the assembled connector unless thediameter of bore portion 41 is increased because the diagonal of a foursided flange is too great for rotation of the flange. However,increasing the diameter of portion 41 seriously weakens the walls of thehousing section 12. Further, in the tuning of the connector it has beenfound that six sides gives a more accurate tuning for reduction ofinsertion loss. The use of a flange with more than six sides ispossible, and gives an even greater tuning accuracy by creating smallerincrements of rotation. However, the increased accuracy is notsufficiently great to justify the increased difficulty in achieving astable and firm seating of the flange. As the number of flange sides isincreased, the periphery thereof approaches a circular configuration,which would possibly be rotatable even when seated. As a consequence, ithas been found that a six sided flange is optimum.

FIGS. 4a and 4 b show a modification of a barrel-ferrule assembly 23 inwhich the sloped or tapered portion 34 has a notch 42 therein foraccommodating a tuning tool, not shown.

FIGS. 5a and 5 b depict, in cross-section, the connector 11 of thepresent invention showing, in FIG. 5a, the flange seated position and inFIG. 5b, the disengaged and rotatable position of the flange for tuning,demonstrating how tuning is achievable with a fully assembled connector.It should be noted that the thickness of the wall 37 is slightly lessthan that of flange 26, thereby insuring that flange 26 can bedisengaged (pushed back) from the seat 36 to where it can be rotatedwithout causing spring 29 to bottom. Connector 11 is shown mounted onthe end of a cable 43 containing a fiber 44, which extend throughconnector 11 as shown.

FIG. 6 is a graph of the effect of offset between two fiber ends (twoconnectors) which is “transverse offset” versus attenuation. For verysmall offsets, such as 0.5 microns (point Y), the loss is correspondingsmall, about 0.05 dB. In the range from zero offset to one micron (pointY′), the loss remains well below 0.3 dB, which is a preferred limit onloss. The next increment range of offset, from one micron to two microns(point Y″) shows an exponential increase in loss, from about 0.22 dB to0.9 dB. Thus, it can be seen that for each incremental increase of onemicron offset, the loss increases exponentially. It can be appreciatedtherefore, that tunability of the connector to decrease the offsetbetween the two fiber ends is highly desirable.

FIG. 7 is a bar chart of the measurements on a group of untunedconnectors showing a wide distribution of insertion loss. It can be seenthat several of the connectors exceed the preferred insertion loss limitof 0.3 dB. FIG. 8 is a bar chart of the same group of connectors aftertuning, showing a compression of the loss distribution to where only oneconnector exceeds the 0.3 dB limit. Thus, from FIGS. 7 and 8, it can beseen that tuning materially enhances the performance of connectors wherethere are eccentricities present, which is virtually always the case.

Tuning Index Tool

FIG. 9 is an exploded perspective view of the tuning index tool 51discussed hereinbefore. Tool 51 comprises a hollow circular member 52having a retaining wall 53 for a warped leaf spring 54. Member 52 has aplurality of openings or windows 56 around the periphery thereof, spacedsixty degrees (60°) apart, and a plurality of keyways 57, only one ofwhich is shown in FIG. 9, which are spaced around the inner periphery ofmember 52 spaced sixty degrees (60°) apart. With reference to FIG. 11,which is a cross-section of tool 51 along the lines A—A of FIG. 10,member 52 has a wall 58 therein, formed by disc member 59 which has aconnector adapter 61 affixed thereto on one side. Extending from theother side of disc 59 is a split sleeve 62, held within adapter 61, forreceiving the ferrule of a connector mounted in adapter 61. Sleeve 62also receives the ferrule of a connector mounted in a second adapter 63which is affixed to a wall 64 of a movable member 66. Disc member 59 hasa circular array of locating holes 67 surrounding a locating ring 68which seats in a circular groove 69 wall 64 of member 66. As best seenin FIG. 11, wall 64 has extending therefrom six locating projections 71which are dimensioned to fit within openings or locating holes 67. Holes67 form a circular array, with the holes spaced sixty degrees (60°)apart, and, importantly, with one of the holes being at zero degrees(0°) relative to the vertical axis of adapter 61. On the other hand,locating projections or pins 71 are in a circular array and spaced sixtydegrees (60°) apart, with one projection or pin 71 being at zero degrees(0°) relative to the vertical axis of adapter 63. The outer edge of wall64 preferably has a locating mark 72 thereon which, as will be apparenthereinafter, is visible through the windows 56 as member 66 is rotatedduring tests. Preferably locating mark 72 is aligned with the verticalaxis of adapter 63 and is, as a consequence, an indicator of the zerodegree (0°) location of adapter 63.

Tool 51 is assembled by spring 54 being placed within member 52 to bearagainst retaining wall 53, as seen in FIG. 11. Movable member 66 is theninserted into member 52 so that wall 64 rests against spring 54. Discmember 59, the periphery of which has projecting key 73, is theninserted into member 52 with the key being inserted into keyways 57, andlatched therewithin by a plurality of peripherally disposed latchingmembers 74 on member 59 and latching slots 76 within member 52. Sleeve62 is fitted within the two adapter sleeves, as shown in FIG. 11. Theassembled tool 51 is shown in FIGS. 10 and 12, and the tool is use isshown in FIG. 13.

In use, as best seen in FIG. 13, a test jumper 81 which terminates in anLC connector, not shown, is inserted into adapter 63. The connector hasa known magnitude of offset or eccentricity greater than the connector82 to be tested for tuning oriented vertically (0°). The orientation canbe 180°, which is also vertical, but the following discussion will bedirected toward the 0° orientation. Preferably the magnitude of theeccentricity relative to the ferrule axis is 1.8 to 3.5 microns. Theconnector 82 to be tuned is inserted into adapter 61 and has a unknownamplitude and direction of eccentricity. With marker 72 showing in oneof the windows, such as, for example, the 0° orientation window, whichmay be indicated by a marking strip 83 affixed on the periphery ofmember 52 (see FIG. 12), insertion loss is measured. The operator thenpulls member 66, which is ridged to give purchase, in the directionindicated by arrow A, against spring 54 until the ferrules of the twoconnectors are disengaged and locating pins 71 are cleared from openings67. The member 66 is then rotated, for example, clockwise (direction B),until the marker 72 appears in the next window 56, in other words,member 66 is rotated 60°, as is connector 63. Insertion loss is againmeasured and recorded. The process is repeated for five more incrementalrotations, and the measured insertion losses will have a maximum and aminimum. It is noted at which incremental position the insertion losswas the least, for example, it was least at the second rotationalposition, which is an indication that 120° of rotation resulted inclosest alignment of the fiber ends. The connector to be tuned is thenremoved from the tool. Suitable means, such as the especially designedspanner wrench previously discussed, is then used to rotate the ferruleof the connector 120° counter-clockwise in the manner explainedhereinbefore, to “tune” the connector. Inasmuch as the eccentricityvector of the test jumper was vertical (0°) during the test, then theeccentricity vector of the product connector is now also vertical, andthe connector junction with the other “tuned”, or vertically orientedeccentricity, connecting member, will exhibit the minimum achievableinsertion loss for that connection.

The tuning index tool as described and shown in the figures is thesubject of U.S. patent application Ser. No. 09/363,908.

Tuning Wrench

As pointed out hereinbefore, after the insertion loss measurements arecompleted and the eccentricity orientation of the connector determined,the product connector must then be tuned to the indicated orientation.The tuning of the connector is discussed in connection with FIGS. 5a and5 b wherein it is shown that the ferrule 27 is pushed into the connectoragainst the force of spring 29 until the flange 26 clears the flangeseating opening 36 sufficiently to allow the ferrule/barrel assembly tobe rotated. This movement of the ferrule may be accomplished by anysuitable means, such as, for example, needle nose pliers which are usedto grip the ferrule and to push it. The ferrule is made of sufficientlyhard material, such as a ceramic, that judicious gripping thereof withpliers is generally insufficient to damage the ferrule. It is desirablethat the assembly not be pushed so far that the spring 29 bottoms, whichcan, over time, weaken the spring or even damage it.

FIGS. 14a through 14 f there are shown several views of a unique tuningwrench 83 for use with the arrangement of FIG. 4a. Wrench 83 has afirst, enlarged, body portion 84 having a hexagonal shape for ease ofgripping. It is to be understood that portion 84 can have other shapesbesides hexagonal; however, the hexagonal shape makes possible an easydetermination of when a 60° rotation has been achieved. Extending fromportion 84 is a limiting member 86 having a diameter greater than bore21 in the front portion of connector 11 and a flat face 87 at its distalend. Extending from face 87 is a strengthening member 88 which has adiameter that is less than the bore 21. A central bore 89 extendsthrough member 84, 86, and 87 as shown. A tubular member 91 is locatedin bore 89 and affixed thereto. Member 91 is preferably made of metal,although it is not intended that it be restricted thereto, since othermaterials may be suitable. The distal end of member 91 has first andsecond tangs 92 and 93, diametrically opposite each other which form aspanner wrench. The inner diameter of member 91 is such that it slideseasily over the ferrule 27 of the connector 11, and tool 83 may then bepushed forward to where the tangs 92 and 93 engage slot 42 of the flangemember 26. It will be obvious to workers in the art that one tang can beused. FIG. 14e depicts this operation just prior to such engagement, andFIG. 14f depicts ferrule 27 in the disengaged position after tool 83 ispushed forward until face 87 butts against the front of the connector,thereby limiting the distance that the ferrule/barrel assembly is pushedagainst the spring. The distance that member 91 protrudes from limitingmember 86 is sufficient to allow tangs 92 and 93 to engage slot 42, plusa distance after such engagement to incur disengagement of flange member26, as seen in FIG. 14f, but no more, face 87 blocking any furtherrearward movement thereof. Body portion 84 preferably has a referencehole 94, located at one of the cusps of the hexagonal shape, and, asseen in FIG. 14b, the plane in which the tangs 92 and 93 lie is normalto the vertical centerline of reference hole 94.

The wrench 83 is primarily intended for use with the tuning index tool51 and is used to make the incremental rotations of the productconnector, the number of increments being indicated by the results ofthe test process discussed hereinbefore. However, the wrench may also beused to make tuning adjustments in the field to the fully assembledproduct connector.

The tuning wrench, as hereindescribed, is the subject of U.S. patentapplication Ser. No. 09/362,203, filed concurrently herewith.

In conclusion of the detailed description, it should be noted that itwill be obvious to those skilled in the art that many variations andmodifications may be made to the preferred embodiment as shown hereinwithout substantial departure from the principles of the presentinvention. All such variations and modifications are intended to beincluded herein as being within the scope of the present invention asset forth in the claims. Further, in the claims hereafter, thecorresponding structures, materials, acts, and equivalents of all meansor step plus function elements are intended to include any structure,material, or acts for performing the functions without specificallyclaimed elements.

What is claimed is:
 1. A fully assembled tunable optical fiber connectorcomprising: on assembly comprising an elongated tubular member having aferrule holding member thereon and a ferrule extending from said holdingmember; a housing member having a central bore extending therethrough inwhich said assembly is located; a spring member bearing against a rearsurface of said holding member and against the housing for applying aforward biasing force to said assembly; characterized in that saidholding member has a multi-faceted periphery and is rotatable withinsaid bore; and said housing member has a multi-faceted seating areawithin said bore, the number of facets on the holding member and theseating area being the same.
 2. The optical fiber connector as claimedin claim 1 wherein said multifaceted holding member has a tapered frontsurface and said seating area has a tapered constriction in said borefor receiving said tapered front surface.
 3. The optical fiber connectoras claimed in claim 2 wherein said tapered front surface has a slottherein.
 4. An optical fiber connector as claimed in claim 1 whereinsaid holding member is hexagonal in shape.
 5. The optical fiberconnector as claimed in claim 1 wherein said seating area has ahexagonal inner periphery.
 6. An optical fiber connector as claimed inclaim 1 wherein said multi-faceted periphery comprises a circular shapehaving a plurality of equally spaced slots therein.
 7. An optical fiberconnector as claimed in claim 6 wherein there are six slots, spacedsixty degrees (60°) apart.
 8. An optical fiber connector as claimed inclaim 1 wherein said seating area has a plurality of splines extendingtoward the central axis and equally spaced about the periphery.
 9. Anoptical fiber connector as claimed in claim 8 wherein there are sixsplines spaced sixty degrees (60°) part.
 10. The optical fiber connectoras claimed in claim 1 wherein said holding member has a firstlongitudinal thickness and said seating area has a second longitudinalthickness, said second thickness being less than said first thickness.11. The optical fiber connector as claimed in claim 1 wherein theconnector is an LC type.
 12. A method of tuning an assembled opticalfiber connector having a housing and an axially movable assembly whichhas a multi-faceted ferrule holding member seatable within the housingcomprising the steps of: mating the connector ferrule in buttingrelationship with the ferrule of another connector; measuring theinsertion loss; unseating the multi-faceted holding member; and rotatingit an incremental amount equal to the angle between two adjacent facetsthen reseating the holding member; measuring the insertion loss;repeating the step of rotating the holding member until the incrementalangles of rotation positions total 360° while measuring the insertionloss at each position; determining the angular position at which theinsertion loss is a minimum; and rotating the assembly to that position.13. A method of tuning an optical fiber connector as claimed in claim 12wherein the connector ferrule is mated in butting relationship to aconnector ferrule having a known direction of its eccentricity vector.14. A method of tuning an assembled optical fiber connector having ahousing and an axially movable assembly which has a multi-facetedferrule holding member seatable within the housing comprising the stepsof: mating the connector ferrule in butting relationship with theferrule of another conductor; measuring the insertion loss; unseatingthe multi-faceted holding member and rotating it an incremental amountequal to the angle between two adjacent facets then reseating theholding member; measuring the insertion loss; repeating the step ofrotating the holding member until the incremental angles of rotationpositions total 360° while measuring the insertion loss at eachposition; determining the angular position at which insertion loss is amaximum; and rotating the assembly to a position 180° from the angularposition where the loss was a maximum.
 15. A method of tuning an opticalfiber connector as claimed in claim 14 wherein the connector ferrule ismated in butting relationship to a connector ferrule having a knowndirection of its eccentricity vector.